The overall goal of this project, led by Prof. Peter Sorger, isto delineate, in precise molecular terms, the mechanisms that regulate the onset of apoptosis in mammalian cells following exposure to small molecule and biological therapeutics. Variation from one cell type to the next and one cell to the next will be an area of particular focus, with the eventual goal of developing means to predict patient-specific responses to therapy. As a means to create mechanistic, probabilistic, integrative and predictive understanding of apoptosis we will collect population-level and single-cell data on caspase activation kinetics and construct, calibrate and analyze a series of mathematical models that describe key steps in mammalian cell death. We will focus largely on existing and investigational anti-cancer drugs, but also expect to examine agents that alter inflammatory and immune responses. Our selection of therapeutic agents is guided by (i) the importance of conventional agents in standard of care cancer treatment and the possibility of developing improved clinical protocols (e.g. taxanes) (ii) the extent of patient-patient variation in drug response and the attendant difficulty of identifying patients who might benefit from a particular treatment (iii) the potential of new agents to significantly improve outcomes as demonstrated by pre-clinical and clinical studies (e.g. ABT-737). Four specific aims will be pursued involving (1) predictive and mechanistic analysis of pathways controlling mitochondrial outer membrane permeablization and effector caspase activation in cells exposed to ligands that trigger extrinisic apoptosis (2) direct comparison of cell-to-cell variation in the timing and probability of cell death among members of a clonal cell population and between different tumor cell lines (3) experimental and model-driven analysis of intrinsic apoptosis induced by the microtubule poison paclitaxel and the Bcl2 inhibitor ABT737 and single-cell analysis of chemotherapeutics used in combination on diverse cancer cell lines (4) development and application of methods for intravital imaging of mitosis and apoptosis in cancer in situ in the mouse. Success with these aims will impact not only the study of apoptosis, but also general cancer biology and the use of chemotherapeutic drugs.